The present invention relates to a method for limiting the working area of a computerized numerical control (CNC) machine tool.
Generally, the working area of a CNC machine tool is determined by specifications of the machine tool. When a tool of the machine tool is beyond the working area, mechanical damage may occur caused by impact to, e.g., a ball screw of a working stage, thus the boundaries of the working area becomes important. In order to limit the working area, limit switches have been installed at the boundaries of the working area.
FIG. 1 is a schematic diagram for explaining a conventional method for limiting the working area of a machine tool. As shown in the drawing, a plurality of limit switch S1, S2, S3 and S4 are arranged around the perimeter of a working area of a working stage 1. The limit switches are for detecting dogs 2 which move according to the movement of the tool (not shown). When a dog 2 is detected by the limit switch S1, S2, S3 or S4, a main controller (not shown) controls a servo controller (not shown) so that a pulse width modulation (PWM) signal is halted and simultaneously dynamic brakes (not shown) come into operation. Accordingly, the tool comes to a stop since the servo motor for transferring the tool ceases to run. Here, since the braking distance of the tool is shorter than the length D1 of the dogs 2, the tool can be safely stopped. The length D1 in a moving direction of the dog 2 is typically between 30-100 mm.
However, such a conventional method of limiting the working area has the following problems.
First, since the working area is determined according to the installation positions of the limit switches S1, S2, S3 and S4, it is difficult to change the boundaries of the working area. FIG. 2 shows an example of a working area 4 set by hardware which is different from the working area 3 which is actually required. According to the conventional working area limiting method, the hardware-set working area 4 appears to be larger than the actually required working area 3 since it is very difficult to change the hardware-set working area 4. Accordingly, the conventional CNC machine tool cannot perform a faster and more accurate control.
Second, since the tool is stopped abruptly by the dynamic brakes when one of the dogs 2 is detected by the switch S1, S2, S3 or S4, the machine tool system may receive an impact.